1. Field of the Invention
The present invention relates to cargo vehicles such as fork lift trucks. More particularly, it relates to a deadman brake assembly which automatically works when the driver is not on his seat.
2. Description of the Prior Art
FIG. 5 shows a typical conventional deadman brake provided on a cargo vehicle such as a fork lift truck. As illustrated, the deadman brake assembly comprises a seat supporting plate 2 for supporting a driver's seat 1 and a brake bar 4 of a drum type brake device 3 connected by a link mechanism 5. When the driver is not on the driver's seat 1, the seat supporting plate 2 pivoted on a bracket 7 of a vehicle frame 6 is tilted forward (the direction of the arrow A) as a result of the action of a tension spring 8, and a brake shoe 9 sandwiches a brake drum 10 on both sides thereof to exert a braking action on the brake drum 10. When the driver sits on the driver's seat 1, the seat supporting plate 2 is tilted against the spring force of the tension spring 8 to the position indicated by the dotted chain line so that the brake drum 10 is released from the state in which it is sandwiched by the brake shoe 9.
As will be apparent from the above, in the deadman brake, the driver's seat 1 always has a tendency to tilt forward as a result of the action of the tension spring 8. However, since the tension spring 8 has a maximum tensile force when the driver sits on the driver's seat 1, the lifting force exerted on the driver's seat when the driver sits on the seat is greater than that exerted when the seat is not occupied. This has resulted in problems that, even when the driver sits on the driver's seat, the seat can be shaky during driving depending on the posture of the driver and the driver can have a sense of floating.